Capillary spark light source



May 17, 1960 w. J. NOLAN, JR

' CAPILLARY SPARK LIGHT SOURCE.

Filed Nov. 9, 1956 FIG 1 5- IO KY 0.6.

POWER SUPPLY United States Patent 2,931,299 CAPILLARY SPARK LIGHT souncuWilliam J. Nolan, Jr., Norco, Califi, assignor t'o Motorola,

Inc., Chicago, Ill., a corporation of Illinois Application November 9,1956, Serial No. 621,324

' 3 Claims. or. 313-113) This invention relates to new and usefulimprovements in electric spark discharge lights and more particularlyto. an improved spark discharge light in which the spark electrodes areenclosed within a capillary passage in a transparent member.

In recent years there have been developed improved electric sparkdischarge lights for producing high intensity flashes of short duration.These spark discharge lights have proved to be very eflective as highintensity light sources'for photographic work, for stroboscopicobservation and for optical range finding equipment. In theelectricspark discharge light, a high voltage power supply is used to charge anelectrical condenser which is then discharged across'a pair of sparkelectrodes. In somespark discharge lights a trigger electrode is used toinitiate an ionized path for the discharge of a spark between the mainspark electrodes. In the development of spark discharge lights as alight source'for optical range measuring equipment one of the problemswhich has arisen and which has not been satisfactorily solved is that ofthe'uncertain location of the spark with respect to the electrodes. Thespark has a tendency to wander over the electrode surface and produces:an erratic and incomplete illumination of the target. If the electrodesare brought to a sharp point the condition may be improved somewhat, butelectrode wear becomes so rapid as to be intolerable and break downvoltage varies substantially from pulse to pulse.

It is therefore one object of this invention to provide an improvedspark discharge light which is capable of producing a high intensityconfined spark.

Another object of this invention is to provide an improved sparkdischarge light in which spark wander is substantially eliminated andthe light is concentrated at approximately half of the sphere to reflectlight back to a selected point.

Other objects and features of this invention will become apparent fromtime to time throughout the specifi- V cation and claims as hereinafterrelated.

In the accompanying drawing, to be taken as a part of thisspecification, there is clearly and fully illustrated a preferredembodiment of this invention in which drawings;

Fig. 1 is a view in cross-section of an improved spark discharge lighthaving electrodes discharging in a capillary passage, and showing onepossible schematic wiring diagram for the light, and

Fig.12 is a detail sectional view of the quartz sphere and capillarypassage therein in which the spark electrodes are positioned,

This invention comprises animproved spark discharge light having a pairof spark discharge electrodes arranged for discharge from a capacitivedischarge circuit. The spark discharge electrodes are positioned in acapillary passage through a sphere of a transparent material such asquartz or the like so that the spark is closely confined in thecapillary passage and spark wander is thus eliminated. The quartz spheremay, if desired, be provided with a reflective coating over a portion ofthe surface to concentrate and reflect light back to the light source orany other selected point. 7

Referring to the drawings by numerals of reference and more particularlyto Fig. 1, there is shown a spark discharge light assembly 10 which isenclosed and supported within a metal casing 12. Casing 12 has ap1urality of openings 14 around the lower end thereof and has aremovable metal plug or end wall 16 at said lower end. A capacitor 18 ispositioned within the upper portionofthe casing 12 andhas' a threadedterminal 20 extending through the end wall of the casing and secured inplace by a threaded nut 22. At the other end of the capacitor 18 thereis a threaded projection 24 constituting the second terminal of thecapacitor on which is supported an electrode holder 26 having a sparkelectrode 28 therein. The electrode holder 26 abuts a spacer member 30which in turn abuts and secures in place a transparent sphere 32 ofglass, quartz, or the like.

I, The sphere 32 has an aperture37 of capillary size therein whichreceives the lower end of the spark electrode 28. The sphere 32 rests ona ring-shaped support 39 on the removable wall or plug 16. A secondspark electrode 341is secured in the re'movablewall or plug 16 andextends in to the capillary opening 37 in the quartz sphere. 32. Thequartz sphere 32., as shown in Fig. 2,

may be provided with a reflecting coating 33 of aluminum or other metalwhich reflects stray light back to the spark zone as indicated by thedotted lines in Fig. 2.

This spark discharge light is energized intermittently from a D.C. powersupply 36 which may provide a voltage of the order of 5,000 to 10,000volts. The power supply 36 is connected as by a lead 38 to the terminal20 on the capacitor 18 and is also connected to ground as indicated at40. The power supply 36 is also connected by a lead 42 to a resistor 44which may have a resistanceof the order of 500,000 ohms. The resistor 44is connected as at 46 to the other terminal of the capacitor 18. Thecapacitor 18 may have a capacitance of the order of 0.1 mid. and berated 5,000 volts.

Operation In operation the power supply 36 is arranged to pro I vide anintermittent source of DC. power to charge the capacitor '18. Thecapacitor 18 when fully charged will discharge through the electrodes 28and 34 to produce a spark discharge 35. The spark discharge 35 isconfined within the capillary passage 37 in the quartz sphere 32 andthus is not permitted to wander about the surface of the sparkelectrodes.

The volume occupied by the spark is a function of the energy dissipatedand if the energy is not sufficient to create a spark large enough tofill the capillary passage then spark wander may still occur. However,when the energy is increased above that necessary to fill the capillarypassage with the spark a substantial increase in brightness is obtainedover the brightness produced by an open spark. With very high sparkenergies, however, it is necessary to use material of substantialthickness to confine a spark within the capillary passage-since the highenergy of the spark may shatter the transparent member through which thecapillary passage 37 extends.

It is necessary to allow a substantial clearance between the electrodes28 and 34 and the walls of the capillary passage 37 so that materialwhich is sputtered off the electrodesduring the spark and productsofdecomposition of the glass or quartz will be blown out of the regionof the spark gap. If this clearance is not provided, the materialsputtered off the electrodes during the spark and products ofdecomposition of the glass will form on the surface of the passage 37 anopaque film which is electrically conducting and which will short'outthe electrodes 28 and 34. This spark light has been successfullyoperated using electrodes .020 inch in diameter, positioned in acapillary passage, .030 inch diameter, and having spark energies ofabout 0.5 joule.

While this spark light assembly is illustrated with a spark electrodepositioned in a capillary passage through a glass or quartz sphere, itis possible to position electrodes in a capillary passage through atransparent member of other shapes such as a cylinder or prism. Thespherical shaped member 32 is preferred, however, for an opticalmeasuring system. Since the usual optical system collects light fromonly a limited angle, it is possible to increase the brightness of thelight source by coating the unused portion of the surface of the spherewith a reflecting material 33 such as aluminum to return the otherwisewasted light to the spark zone. The efiectiveness of this reflectorcoating of course depends on the absorption characteristics of thespark. While the sphere 32 has been described as being formed of glassor quartz, other materials such as sapphire or other transparentcrystalline material may be desired because of considerations ofmechanical strength and of light transmittance requirements of theoptical system in which this light is used.

I claim:

1. A spark discharge device including in combination, a transparentspherical member having a capillary passage extending therethrough alonga diameter thereof, and a pair of spark electrodes positioned in saidpassage and forming a spark gap at substantially the center of saidspherical member, said spark electrodes being adapted to be connected ina high voltage circuit to produce a spark discharge at said gap, withthe discharge 5 path being defined by said passage to prevent sparkWander, said electrodes being spaced slightly from the surface of saidpassage to provide an escape path for erosion products caused by saidspark discharge.

2.. A spark discharge device including in combination, a transparentmember having a spherical outer surface and a capillary passage therein,a pair of spark electrodes positioned in said passage and adapted to beconnected in a high voltage circuit to produce a spark discharge in saidpassage, said electrodes being spaced from the surface of said passageto provide an escape path for erosion products, and a reflective coatingon a portion of said spherical surface of said transparent member forreflecting light radiation and returning the same to said passage.

3. A spark discharge device including in combination, a transparentmember having a spherical outer surface and a cylindrical capillarypassage therein, a pair of spark electrodes positioned in said passageand adapted to be connected in a high voltage circuit to produce a sparkdischarge between said electrodes, with the dis charge path beingdefined by said passage to prevent spark wander, said electrodes beingsubstantially smaller in diameter than said passage to provide an escapepath for erosion products, and a reflective coating on a portion of saidspherical outer surface of said transparent member for reflecting lightradiation and concentrating the same in said capillary passage toincrease the temperature therein and thereby increase the brightness oflight radiation.

References Cited in the file of this patent UNITED STATES PATENTS2,154,542 Swanson Apr. 18, 1939 2,222,093 Swanson Nov. 19, 19402,391,611 Back Dec. 25, 1945 2,775,718 Dubilier Dec. 25, 1956

